1. Field of the Invention
This invention relates to bubble domain detectors and, in particular, large output, chevron stretcher detectors capable of reading a first bit, as well as subsequent bits, adjacent to the detection element in a start/stop mode.
2. Description of Prior Art
There are many known bubble domain devices and systems in the art. These systems and devices are fabricated on various types of magnetic bubble domain supporting material. One of the existing materials is SmGaYIG. In this type of material, for example, as well as others, it is known that due to finite wall mobility of a strip or a bubble the expansion of a bit in a long chevron stretcher detector requires several rotating field cycles. For example, expansion rates for 16 .mu. devices indicate that in one field rotation the bubble strip expands about 100 chevrons. Typical sensitivities for this length of stretch or expansion are about 1.10 mv./ma. As a result, the output signals produced by these devices are limited to about 5 mv. at room temperature or about 2.5-3 mv. over a temperature range of approximately -10.degree. to + 70.degree. C. Consequently, the associated sense amplifier is limited to having a threshold below 2.5 mv. which restricts the choice of integrated circuit and limits the signal to noise ratio.
Moreover, it is highly desirable that this relatively large output signal be provided within the first cycle after start-up (when the memory is operated in the start-stop mode.) That is, it is desirable to be able to detect the bit immediately adjacent to the detector upon energizing the rotating fields coils. Simply making the detector longer than 100 elements fails to accomplish this goal because the bubble mobility limits the strip length to 100 or less over the operating bias range.